We are developing improved methods for assessing the health of sperm, both for application to reproductive toxicology studies and for development of improved biomarkers for human male fertility. Work has progressed in three areas: (1) developing new methods for characterizing the short-term motility of individual sperm; (2) developing methods for comparing samples of populations of sperm, i.e. sets of specimens; and (3) developing experimental protocols to quantify sperm diffusion dynamics over longer time frames. Proper characterization of the motion of sperm is needed to detect and interpret effects of male exposures to reproductive toxicants. Large numbers of sperm can be individually tracked using computer-assisted semen analysis (CASA), which records X-Y coordinates of the planar projection of the sperm's path over approximately one second, and outputs seven summary measures describing that track. Our method reduces the required number of measures to three, and includes assessment of the predictability of the path. Applied to a toxicologic data set, our three measures discriminated between normal and abnormal sperm as well as did the seven CASA measures. Moreover, our predictability measure improved discrimination between the treated and untreated sperm above what was achievable based on the CASA measures alone. Many individual sperm are studied for each animal/specimen in an experiment. I have developed a model that enables testing for effects on multiple measures of motility and allows estimation of a specimen-specific motility score. The third project, development of improved experimental protocols to study diffusion over a longer time scale (perhaps minutes) is just beginning.